1. Field of the Invention
This invention relates to a circuit-constituting member for forming a power circuit in a vehicle such as an automobile.
2. Description of the Related Art
As a conventional unit for distributing electric power to electronic units from a common on-vehicle power source,there has been known an electric connection box in which a plurality of bus bar boards are stacked together to form a power feed circuit, and fuses and relay switches are incorporated thereinto.
In recent years, in order to achieve a compact design and high-speed switching control of such an electric connection box, there has been developed an electric connection box in which instead of using the relays, semiconductor switching devices such as a FET are provided between input and output terminals.
For example, JP-A-10-35375 discloses an electric connection box which includes a bus bar board forming a current circuit, FETs (semiconductor switching devices) incorporated into the current circuit, and a control circuit board for controlling the operation of the FETs. The bus bar board and the control circuit board are arranged at two (upper and lower) stages in spaced relation to each other. The FETs are disposed between the two boards. Drain terminals and source terminals of the FETs are connected to the bus bar board while gate terminals of the FETs are connected to the control circuit board.
In the electric connection box disclosed in the above publication, there are needed at least two boards, that is, the bus bar board and the control circuit board. Besides, there must be secured a space for allowing these boards to be arranged in a three-dimensional manner in spaced relation to each other so that the FETs can be provided between the two boards. Also, in the above electric connection box, the FETs are provided between the bus bar board and the control circuit board. Therefore heat generated from the FETs is liable to remain in the space between the two boards. It is necessary to adopt a complicated structure for radiating this heat. Also, a complicated and large radiating member, having many fins for radiating purposes, must be used.